Deformation and failure mechanisms of electrochemically lithiated silicon thin films

A fundamental understanding of mechanical behavior of a Li-Si system is necessary to address the poor mechanical integrity of amorphous silicon (a-Si) electrodes, in order to utilize their enormous capacity in Li-ion batteries. In this work, deformation and failure mechanisms of electrochemically lithiated a-Si thin films were investigated using nanoindentation and molecular dynamics simulation techniques. The cracking observed in the a-Si thin films after the initial lithiation-delithiation cycle is associated with the tension stress developed when constrained by the substrates. The MD simulations provide an atomistic insight on the origin of plasticity and transition of fracture mechanisms with increasing lithium concentration in the electrode. Both experiment and the MD simulations indicate reduced strength, elastic modulus but increased ductility in the a-Si films after the full lithiation-delithiation cycle, as a result of increased disorder in the microstructures. Also, the mapping of void nucleation and growth indicates different failure modes in pristine and delithiated a-Si.